Virtual storage system and control method thereof

ABSTRACT

A virtual storage system is equipped with a plurality of storage systems and a virtualization device for virtualizing the plurality of storage systems logically into a single storage resource provided to a host computer. When one of the storage systems receives a command from the host computer, in the event that the storage system itself is not in possession of a function corresponding to the command, the storage system retrieves a storage system in possession of a function corresponding to the command and transfers this command to the storage system in possession of the function corresponding to the command.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/732,304,filed Mar. 26, 2010, which, in turn, is a continuation of applicationSer. No. 11/389,128, filed Mar. 27, 2006 (now U.S. Pat. No. 7,711,908);and which application relates to and claims priority from JapanesePatent Application No. 2006-34882, filed on Feb. 13, 2006, the entiredisclosures of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a virtual storage system and controlmethod thereof for virtualizing a plurality of storage systems logicallyas a single storage resource.

In the storage field, notice is being taken of “storage grids (wide areawide band shared file systems)” capable of achieving high processingperformance and fault tolerance that operate in such a manner that aplurality of computing resources distributed over a network operate as asingle computing resource. A method of virtualizing a plurality ofstorage systems logically as a single virtual storage resource iswell-known as a storage grid operation method.

Technology where a logical unit of a second storage system existingoutside of a first storage system is managed within the first storagesystem is well-known as technology for virtualizing a volume (refer toJapanese Patent Laid-open Publication No. Hei. 7-210439, Japanese PatentLaid-open Publication No. 2001-318833, or Japanese Patent Laid-openPublication No. 2004-220450).

SUMMARY

At a storage grid, when a storage system having function B of aplurality of storage systems logically constituting a single storageresource receives a processing request for function B from a hostcomputer, this storage system is capable of recognizing the processrequest for function B and carrying out processing.

However, the respective storage systems that are virtualized logicallyas a single storage resource by the storage grid are not limited tohaving to share functions. For example, there are also cases where onlysome of the storage systems of the plurality of storage systemsconstituting the storage grid have function A. The host computerrecognizes the plurality of storage systems as a single storageresource. There are therefore cases where process requests for functionA are sent to storage systems that do not have function A. In suchcases, a command error is sent back to the host computer, and processrequests for the function A are not processed appropriately.

The present invention therefore deals with the problem of processingcommands from a host computer in an appropriate manner even in caseswhere the functions in the possession of each storage system aredifferent in a virtual storage system virtualizing a plurality ofstorage systems as a single storage resource.

In order to resolve the aforementioned problems, a virtual storagesystem of the present invention having a plurality of storage systemsand a virtualization layer for virtualizing the plurality of storagesystems logically into a single storage resource provided to a hostcomputer comprises a storage section for storing a correspondingrelationship between commands issued by the host computer, functionscorresponding to the commands, and storage systems in possession of thefunctions, a retrieval section for retrieving storage systems inpossession of functions corresponding to the commands from the pluralityof storage systems and a transfer section for transferring the commandsto the storage systems in possession of the functions corresponding tothe commands.

According to the present invention, it is possible to process commandsfrom a host computer in an appropriate manner even in cases where thefunctions in the possession of each storage system are different invirtual storage systems virtualizing a plurality of storage systems as asingle storage resource.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration view of a virtual storage system ofthis embodiment.

FIG. 2 is a view illustrating a same device correspondence table.

FIG. 3 is a view illustrating each of the various programs and tablesstored in the storage system.

FIG. 4 is a view illustrating a command-function correspondence table.

FIG. 5 is a view illustrating a function-device correspondence table.

FIG. 6 is a view illustrating a function possessed by a storage system.

FIG. 7 is a further view illustrating a function possessed by a storagesystem.

FIG. 8 is a view illustrating a device information table.

FIG. 9 is a view illustrating fault information.

FIG. 10 is a flowchart showing a typical command process.

FIG. 11 is a flowchart showing command management executed by a virtualstorage system.

FIG. 12 is a flowchart showing further command management executed by avirtual storage system.

FIG. 13 is a flowchart showing command management executed by a hostcomputer.

FIG. 14 is a flowchart showing command management executed by a virtualdevice.

FIG. 15 is a flowchart showing command management executed by a masterservice processor.

FIG. 16 is a flowchart showing command management using a commanddevice.

FIG. 17 is a flowchart showing a process for carrying out commandmanagement as a result of a host computer re-issuing a command.

FIG. 18 is a flowchart showing a process at the time of a faultoccurring during transfer of a command.

FIG. 19 is a flowchart showing a further process for when a fault occursduring transfer of a command.

FIG. 20 is a flowchart showing a load distribution process for a virtualstorage system.

FIG. 21 is a view illustrating specification information.

FIG. 22 is a flowchart showing a command process taking intoconsideration differences in performance of each storage system.

FIG. 23 is a view illustrating rate of operation information.

FIG. 24 is a flowchart showing a command process taking intoconsideration differences in rate of operation of each storage system.

FIG. 25 is a system configuration view of a virtual storage system ofthis embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a system configuration of a virtual storage system 100 ofan embodiment. The virtual storage system 100 is equipped with aplurality of storage systems 20A, 20B, 20C, and an external storagesystem 70.

One or more host computers 51 are connected to the storage systems 20A,20B, 20C, respectively. A host computer 51 having a virtualizationprogram 63 is connected to the storage systems 20A, 20B, 20C via a SAN(Storage Area Network) 41 and recognizes the plurality of storagesystems 20A, 20B, 20C logically as a single storage resource(hereinafter referred to as virtual storage system 100) due to thefunction of the virtualization program 63.

Another host computer 51 that does not have a virtualization program 63is connected to the storage systems 20A, 20B, 20C via SAN 42, avirtualization device 52, and SAN 41 and recognizes the plurality ofstorage systems 20A, 20B, 20C as a single virtual storage system 100using a function of the virtualization program 63 within thevirtualization device 52.

From the above configuration, the host computer 51 recognizes storageregions provided by the plurality of storage systems 20A, 20B, 20Clogically as a single virtual storage system 100 and is capable ofaccessing the virtual storage system 100.

The virtualization device 52 virtualizes the storage regions providedrespectively by the plurality of storage systems 20A, 20B, 20C logicallyinto a single storage region. The virtualization device 52 may be, forexample, a virtualization switch, an intelligent switch, or avirtualization-dedicated device, etc. A system configured so as toinclude the virtual storage system 100 and the virtualization device 52is referred to as a storage network system.

The host computer 51 is comprised of an application program 60 andalternate path software 61.

The application program 60 is, for example, a service program such as,for example, database management software, Web application software,streaming application software, and E-business application software,etc.

The alternate path software 61 manages logical paths between the hostcomputer 51 and logical devices within the virtual storage system 100and executes multipath control. Multipath control refers to controllingof which logical path of a plurality of logical paths is used to accessa logical device. The alternate path software 61 is comprised of amultipath management program (not shown), an inter-casing multipathprogram (not shown), a priority control program (not shown), and a samedevice correspondence table 62.

The multipath management program carries out management and control ofthe whole of the alternate path software 61.

The inter-casing multipath program recognizes a plurality of logicalpaths connected to a logical device 701 within an external storagesystem 70 via a plurality of storage systems 20 as a multipath.

The priority control program selects logical paths to be given priorityfor use from a plurality of logical paths based on the respective usagerates of a plurality of logical paths connected to the same logicaldevice.

The same device correspondence table 62 shows the correspondingrelationship between logical paths and logical devices in a networkenvironment where different logical paths are connected to the samelogical device.

It is not essential for the alternate path software 61 to be storedwithin the host computer 51 and this may also be stored within thevirtualization device 52.

In the description below, the storage systems 20A, 20B, 20C are referredto as “storage system 20” when there is no particular need fordiscrimination.

The storage system 20 is comprised of a CPU (Central Processing Unit)21, memory 22, a disc interface control section 23, a disc unit 24, FC(Fiber Channel) interface control sections 25, 26, and LAN (Local AreaNetwork) interface control sections 27, 28.

The CPU 21 executes each of the various control processes occurring atthe storage system 20 by executing each of the various programs andmodules stored in the memory 22. The memory 22 is referred to as aninternal storage device, and is comprised of non-volatile memory forstoring each of the various modules etc., and volatile memory fortemporarily holding computation processing results of the CPU 21.

The CPU 21 is connected to the disc unit 24 via the disc interfacecontrol section 23. The disc interface control section 23 convertslogical addresses outputted by the CPU 21 to LBA (Logical BlockAddresses) and is capable of accessing a logical device using the CPU21.

The disc unit 24 has a plurality of disc drives 240 constituting a RAID(Redundant Arrays of Independent Inexpensive Disks).

The disc drives 240 are physical devices such as an FC (Fibre Channel)disc drive, a SATA (Serial Advanced Technology Attachment) disc drive, aPATA (Parallel Advanced Technology Attachment) disc drive, a FATA(FibreAttached Technology Adapted) disc drive, an SAS (Serial Attached SCSI)disc drive, or an SCSI(Small Computer System Interface)disc drive, etc.A physical device is a real device having a real storage region.

A logical device 242 is a virtual storage device that does not have areal storage region, with a real storage region storing the dataexisting in the logical device 701 within the external storage system70. Namely, the storage system 20 incorporates the logical device 701 ofthe external storage system 70 as its own internal device and suppliesthis as a logical unit to the host computer 51. In the event that thehost computer 51 is a UNIX (registered trade mark) family system, thelogical unit correlates to a device file (Device File). In the eventthat the host computer 51 is a Windows (registered trade mark) familysystem, the logical unit correlates to a drive letter (Drive Name). ALUN (Logical Unit Number) is assigned to a logical unit. The details ofthe method for virtualizing the logical device 701 of the externalstorage system 70 so as to be handled as an internal device of thestorage system 20 are disclosed in Japanese Patent Laid-open PublicationNo. 2005-107645.

The command device 243 is a dedicated logical unit for handing overcommands and statuses between the host computer 51 and the storagesystem 20. Commands sent from the host computer 51 to the storage system20 are written to the command device 243. The storage system 20 executesprocesses corresponding to commands written to the command device 243and writes the results of execution to the command device 243 asstatuses. The details of the command management using the command device243 are described in the following.

The disc interface control section 23 is capable of controlling theplurality of disc drives 240 using RAID levels (for example, 0, 1, 5)defined by the RAID system. The RAID system manages a plurality of discdrives 240 as a single RAID group. A RAID group is configured from, forexample, four disc drives 240 grouped together into one set (3D+1P), oreight disc drives 240 grouped together into one set (7D+1P).Namely, thestorage regions respectively provided by the plurality of disc drives240 are gathered together to make up a single RAID group. A plurality oflogical devices 241 constituting access units from the host computer 51are defined on a RAID group. One or more logical devices 241 are thenmapped on a logical unit constituted by a logical storage regionrecognized by the host computer 51. The host computer 51 is capable ofaccessing the logical device 241 by designating LUN and LBA.

It is by no means essential to provide the disc unit 24 and the discinterface control section 23 providing that the storage system 20 canprovide storage regions of the external storage system 70 to the hostcomputer 51 by connecting to the external storage system 70.

The FC interface control section 25 controls transfer of commands anddata via SAN 43 between the storage system 20 and the external storagesystem 70. The FC interface control section 26 controls transfer ofcommands and data via SAN 41 between the storage system 20 and the hostcomputer 51. The data communication for via the SAN 41 and 43 is a fiberchannel protocol or iSCSI protocol, etc. SAN 43 is not essential, andthe FC interface control section 25 and external storage system 70 mayalso be directly connected by optical fiber cable etc.

The LAN interface control section 27 is connected to a management server50 via a management network 40. The management network 40 is a LANconfigured from Ethernet cable, etc. The data communication protocol forthe management network 40 is TCP/IP. The management server 50 managesthe production of logical units within the virtual storage system 100,the allocation of logical units to the host computer 51, and the setting(LUN masking, zoning, etc.) of access paths between the host computer 51and the virtual storage system 100.

The external storage system 70 has one or more disc drives 700 in a RAIDconfiguration. The disc drive 700 is a storage device such as an FC(Fibre Channel) disc drive, a SATA (Serial Advanced TechnologyAttachment) disc drive, a PATA (Parallel Advanced Technology Attachment)disc drive, a FATA (Fibre Attached Technology Adapted) disc drive, anSAS (Serial Attached SCSI) disc drive, or an SCSI(Small Computer SystemInterface)disc drive, etc. A logical device 701 is formed on theplurality of disc drives 700.

The external storage system 70 may be a different type of storage systemas the storage system 20 or may be the same type of storage system.

When an access request is received from the host computer 51, thestorage system 20 determines whether this access request is an accessrequest to logical device 241 taken as its own internal device or anaccess request to logical device 701 taken as an external device. Ifthis is an access request to the logical device 701, address conversionis carried out for between the logical device 242 and the logical device701 and an access request to the logical device 701 is sent to theexternal storage system 70.

The service processor 81 is a computer terminal for settingconfiguration information (including a device information table 106 andconfiguration information 108 described later) of the storage system 20and acquiring operation information etc. The service processor 81 isconnected to the LAN interface control section 28 within the storagesystem 20. Each service processor 81 connected to each storage system 20is connected to one master service processor 82. The master serviceprocessor 82 uniformly manages information (configuration information,operation information etc. for the storage system 20) collected fromeach of the service processors 81. One of the plurality of serviceprocessors 81 may function as the master service processor, or eachstorage system 20 may be directly connected to the master serviceprocessor 82.

The virtual storage system 100 exhibits a range where transfer ofcommands and execution of volume migration between each of the storagesystems 20 is possible by transmitting and receiving configurationinformation between each of the storage systems 20. In the event thatthe external storage system 70 is connected to each storage system 20,the range of the virtual storage system 100 includes the plurality ofstorage systems 20 and the external storage system 70. In the event thatthe external storage system 70 is not connected to each storage system20, the range of the virtual storage system 100 includes the pluralityof storage systems 20 but does not include the external storage system70.

Each storage system 20 is capable of being configured as a disc arraysystem provided with a plurality of disc drives 240 in, for example, aRAID configuration, or is capable of being configured as a virtualswitch where each storage system 20 itself constitutes a SCSI target. Astorage system 20 may also be referred to as a storage control device.

The management network 40 is connected to one or more host computers 51.Further, one or more client computers 30 are connected to the managementnetwork 40. Each client computer 51 is connected to a host computer 51via the management network 40 and is capable of requesting input andoutput of data to the virtual storage system 100 via the applicationprogram 60.

FIG. 2 shows a same device correspondence table 62. The same devicecorrespondence table 62 stores a “path number”, “storage systemidentifier”, “LUN”, and “device identifier” in a correlating manner.

“Path number” indicates the number of a logical path.

“Storage system identifier” indicates information for uniquelyidentifying a storage system 20 or external storage system 70 within thevirtual storage system 100.

“LUN” indicates a logical unit number for within the storage system 20or the external storage system 70.

“Device identifier” indicates information for uniquely identifyinglogical devices 241, 242, 701 within the virtual storage system 100.

Three logical paths of path numbers 0, 2, 3 pass through differentstorage systems 20 but are shown to be connected to the same logicaldevice. LUN is different every storage system 20 even for the samelogical device because a host storage domain is adopted.

The same device correspondence table 62 holds a virtualization layer (inthe example shown in FIG. 1, host computer 51 or virtualization device52) virtualizing the plurality of storage systems 20 into a singlevirtual storage system 100.

FIG. 3 shows the various programs and tables stored in the memory 22. Anoperating system 101, function registration program 102, function-devicecorrespondence recognition program 103, command-function correspondencetable 104, function-device correspondence table 105, device informationtable 106, fault information 107, and configuration information 108 arestored in the memory 22.

The command-function correspondence table 104 holds a correspondencerelationship between commands issued by the host computer 51 andfunctions corresponding to these commands. For example, snapshots,replications, and remote copies exist as specific examples of“functions” requested by the host computer 51 to the virtual storagesystem 100.

The function registration program 102 registers command and functioncorrespondence information in a command-function correspondence table104.

The function-device correspondence table 105 holds a correspondencerelationship for functions required by the host computer 51 and storagesystems 20 in possession of these functions.

The function-device correspondence recognition program 103 registers acorrespondence relationship between the storage systems 20 and thefunctions in the function-device correspondence table 105.

The device information table 106 holds attributes of logical devices.

The fault information 107 holds fault information for each storagesystem 20.

The configuration information 108 is mapping information indicating acorresponding relationship between the physical device 701 within theexternal storage system 70 and the logical devices 242 within eachstorage system 20. The details of mapping information for mapping theexternal device at the internal devices is disclosed in Japanese PatentLaid-open Publication No. 2005-107645.

In command management described in the following, it is by no meansessential for the virtual storage system 100 to hold a correspondingrelationship for the commands, functions, and storage systems 20 in thetable format described above providing that which function a commandissued by the host computer 51 corresponds to and which storage system20 has this function can be retrieved, and it is possible for thiscommand to be transferred to the retrieved storage system 20. Forexample, the corresponding relationship for the commands, functions andstorage system 20 can be held as a list structure or other format.

FIG. 4 shows the command-function correspondence table 104. Thecommand-function correspondence table 104 holds a correspondencerelationship between commands issued from the host computer 51 to thevirtual storage system 100 and functions corresponding to thesecommands. For example, command C001 is a command for calling function Aat the virtual storage system 100.

FIG. 5 shows a function-device correspondence table 105. Thefunction-device correspondence table 105 holds a correspondencerelationship for functions required by the host computer 51 and storagesystems 20 in possession of these functions. For example, storage system20A has function B.

As shown in FIG. 6, for example, in the event that the virtual storagesystem 100 is configured from storage system 20A and storage system 20B,storage system 20A and function B, and storage system 20B and function Bare registered in a respectively correlating manner in thefunction-device correspondence table 105, and command C004 and functionB are registered in a correlating manner in the command-functioncorrespondence table 104. Program P4 is for implementing function B. Asshown in FIG. 7, when a storage system 20C is newly added to the virtualstorage system 100, storage system 20C and function A are added so as tobe registered in a correlating manner at the function-devicecorrespondence table 105, and commands C001, C002, C003 and function Aare added so as to be registered in a correlating manner to the commandfunction correspondence table 104. Program P3 is for implementingfunction A.

The following variations in (1) to (6) can be considered as ways for thevirtual storage system 100 to hold the command-function correspondencetable 104 and the function-device correspondence table 105.

(1) The memory 22 within the storage system 20 and the management server50 are respectively held in the command-function correspondence table104 and the function-device correspondence table 105.

(2) The management server 50 holds the command-function correspondencetable 104 and the function-device correspondence table 105.

(3) The host computer 51 holds the command-function correspondence table104 and the function-device correspondence table 105.

(4) A virtualization layer virtualizing a plurality of storage systems20 into a single virtual storage system 100 is held in command-functioncorrespondence table 104 and function-device correspondence table 105.

(5) The service processor 81 and master service processor 82 are held incommand-function correspondence table 104 and function-devicecorrespondence table 105.

(6) The command device 243 holds the command-function correspondencetable 104 and the function-device correspondence table 105.

FIG. 8 shows the device information table 106. The device informationtable 106 is for holding attributes of logical devices and is stored inthe memory 22 within the storage system 20. The device information table106 stores a “device number”, “status flag”, and “external device flag”in a correlating manner.

“Device number” is information for uniquely identifying logical devices241, 242 within a storage system 20.

“Status flag” indicates whether the logical devices 241, 242 within thestorage system 20 are used or not used (empty). “ON” in the drawingindicates that the logical devices 241 and 242 are being used.

“External device flag” indicates whether or not the logical device 242within the storage system 20 is being used as an external device(logical device 701). “ON” in the drawing indicates that the logicaldevice 242 is being used as an external device. “OFF” in the drawingindicates that the logical device 241 is being used as an internaldevice. The default value of the external device flag is “OFF”, and“OFF” is changed to “ON” when the logical device 242 within the storagesystem 20 is mapped to the logical device 701 within the externalstorage system 70.

FIG. 9 shows fault information 107. Fault information 107 is informationindicating whether or not each storage system 20 is functioning normallyor has a fault. In this embodiment, an example is shown where it isdetermined that a fault is occurring at a storage system 20 in the eventthat the storage system is in a state where commands from the hostcomputer 51 cannot be received, but it is also possible to determinewhether or not a fault is occurring at a storage system 20 based on apreset fault level. The fault level used in fault determination may beinputted by the user, or may be a fault level selected by a user from aplurality of fault levels designated by a user. Each memory 22 of eachstorage system 20 and the management server 50 hold the faultinformation 107.

Typical command processes executed by the storage system 20 aredescribed with reference to FIG. 10.

When a command is received from the host computer 51 (S101), the storagesystem 20 determines whether or not the logical device receiving theaccess request is an external device (logical device 701) by referringto device information table 106 (S102).

If the logical device receiving the access request is an internal device(logical device 241) (S102: NO), the storage system 20 accesses theinternal device using normal operations (S103).

If the logical device receiving the access request is an external device(logical device 701) (S102: YES), the storage device 20 sends a commandfor accessing the external device to the external storage system 70(S104).

Next, a description is given with reference to FIG. 11 of commandmanagement executed by the virtual storage system 100. Here, an exampleis shown where, in the event that the storage system 20 receiving thecommand from the host computer 51 does not have a function correspondingto this command, a storage system 20 having this function is searchedfor and the command is transferred to the retrieved storage system 20.

The following (1) to (2) are presumed in the description of FIG. 11.

(1) Each storage system 20 and the management server 50 are respectivelyheld in the command-function correspondence table 104 and thefunction-device correspondence table 105.

(2) A storage system 20C having the function A is newly added to thevirtual storage system 100 comprised of storage system 20A and 20Bhaving the function B.

A process to add storage system 20C to the virtual storage system 100 isthen carried out (S201). Namely, a process to connect the storage system20C to the SAN 41 and recognize the host computer 51 and thevirtualization device 52 (for example, recognition of a storage systemidentifier of the storage system 20C, recognition of the LUN of alogical unit within the storage system 20C, and recognition of a pathnumber of a logical path connecting to this logical unit, etc.) iscarried out. In the event that the storage system 20C shares the logicaldevice 701 of the external storage system 70, the storage system 20 maybe connected to SAN 43.

Next, the management server 50 recognizes that a storage system 20C isnewly added to the virtual storage system 100, recognizes that thestorage system 20C has a program P3, additionally registers a function Ato the command-function correspondence table 104 managed by itself, andadditionally registers storage system 20C to the function-devicecorrespondence table 105 managed by itself (S202).

Information to the effect that the storage system 20C has a program P3corresponding to function A may be acquired as a result of input by auser to the management server 50, or may be acquired from a programduring installation of this program (program sending commands to programP3) corresponding to program P3 to the host computer 51.

Next, the management server 50 notifies the respective storage systems20A, 20B that a program P3 possessed by the storage system 20C has beennewly added to the virtual storage system 100 (S203). As a method ofnotifying the storage systems 20A, 20B that a new function has beenadded, the storage systems 20A, 20B may be notified by the managementserver 50 individually, the management server 50 may notify a specificstorage system 20, or a specific storage system 20 may notify anotherstorage system 20.

Next, the respective storage systems 20A, 20B additionally register thestorage system 20C and the function A to the function-devicecorrespondence tables 105 held within their own memories 22 in acorrelating manner, and additionally register commands C001, C002, C003and function A in the command-function correspondence table 104 in acorrelating manner (S204).

Next, the management server 50 notifies the storage system 20C of acorresponding relationship of existing functions (programs) within thevirtual storage system 100, commands corresponding to these functions,and storage systems 20 having these functions (S205).

After this, the storage system 20C additionally registers storagesystems 20A, 20B and function B in a correlated manner to thefunction-device correspondence table 105 held within its own memory 22and additionally registers command C004 and function B in a correlatingmanner to command-function correspondence table 104 based on information(the correspondence relationship of existing programs (functions) withinthe virtual storage system 100 and storage systems 20 having theseprograms), notification of which was given by the management server 50(S206).

Next, the host computer 51 sends command C001 corresponding to programP3 to the virtual storage system 100 (S207). The host computer 51 doesnot transmit the command C001 while individually recognizing theindividual storage systems 20A, 20B, 20C. Which of the storage systems20A, 20B and 20C receives the command is therefore decided on a case bycase basis. Here, the description is continued assuming the case thatthe storage system 20A receives the command C001.

When command C001 is received, the storage system 20A retrieves whichprogram the command C001 corresponds to and which storage system 20 isin possession of this program by referring to the command-functioncorrespondence table 104 and the function-device correspondence table105 held within its own memory 22 (S208).

If the storage system 20C has received the command C001, the storagesystem 20C implements the steps S210 and S212 described in thefollowing.

Next, the storage system 20A transfers command C001 to the storagesystem 20C via SAN 43 (S209). At this time, in the event that real dataintended to be processed by command C001 exists in the storage system20A, the storage system 20A sends the real data to the storage system20C. Transmission of the real data may take place collectively a singletime or may be carried out partially split across a plurality of times.In the event that real data the command C001 intends to process existsin the logical device 701 of the external storage system 70, supervisionof control of the logical device 701 is changed from the storage system20A to the storage system 20C.

The storage system 20A may also hold information correlating the commandand the storage system 20 of the transfer destination as commandtransfer history information and then transfer a command to anotherstorage system 20 by referring to this history information when a newcommand is received from the host computer 50.

Next, the storage system 20A notifies the host computer 51 of normalreceipt of a command (S210).

After this, the storage system 20C notifies the storage system 20A ofcompletion at the stage where processing of command C001 is complete(S211).

The storage system 20A receiving notification of completion from thestorage system 20C then notifies the host computer 51 that theprocessing of command C001 is complete (S212).

As a further method of command management shown in FIG. 11, a methodexists where, for example, execution of the steps takes place in theorder of step S201, S202, S205, S206, the storage system 20C notifiesthe storage systems 20A, 20B that program P3 and storage system 20C havebeen newly added, step S204 is then implemented, and execution of S207to S212 then takes place in order.

Next, a description is given with reference to FIG. 12 of furthercommand management executed by the virtual storage system 100. Here, anexample is shown where, in the event that the storage system 20receiving the command from the host computer 51 does not have a functioncorresponding to this command, the management server 50 is interrogatedas to which storage system 20 has this function. The management server50 receiving this interrogation retrieves the storage system 20 havingthe function corresponding to this command and notifies the storagesystem 20 that is the destination of this interrogation. The storagesystem 20 receiving notification from the management server 50 thentransfers the command to the storage system 20 having the functioncorresponding to this command.

The following (1) to (2) are presumed in the description of FIG. 12.

(1) It is necessary for the management server 50 to hold thecommand-function correspondence table 104 and the function-devicecorrespondence table 105 but it is not necessary for each storage system20 to hold the command-function correspondence table 104 and thefunction-device correspondence table 105.

(2) A storage system 20C having the function A is newly added to thevirtual storage system 100 comprised of storage system 20A and 20Bhaving the function B.

A process to add storage system 20C to the virtual storage system 100 isthen carried out (S301). Namely, a process to connect the storage system20C to the SAN 41 and recognize the host computer 51 and thevirtualization device 52 (for example, recognition of a storage systemidentifier of the storage system 20C, recognition of the LUN of alogical unit within the storage system 20C, and recognition of a pathnumber of a logical path connecting to this logical unit, etc.) iscarried out. In the event that the storage system 20C shares the logicaldevice 701 of the external storage system 70, the storage system 20 maybe connected to SAN 43.

Next, the management server 50 recognizes that a storage system 20C isnewly added to the virtual storage system 100, recognizes that thestorage system 20C has a program P3, additionally registers a function Ato the command-function correspondence table 104 managed by itself, andadditionally registers storage system 20C to the function-devicecorrespondence table 105 managed by itself (S302).

Next, the host computer 51 sends command C001 corresponding to programP3 to the virtual storage system 100 (S303). The host computer 51 doesnot transmit the command C001 while individually recognizing theindividual storage systems 20A, 20B, 20C. Which of the storage systems20A, 20B and 20C receives the command is therefore decided on a case bycase basis. Here, the description is continued assuming the case thatthe storage system 20A receives the command C001.

Next, upon receiving the command C001, the storage system 20A determineswhether or not it is itself in possession of function A capable ofexecuting command C001. In this embodiment, the storage system 20A isnot in possession of function A capable of executing command C001 andtherefore interrogates the management server 50 as to which storagesystem 20 is in possession of the function A capable of executingcommand C001 (S304).

If the storage system 20A is in possession of the function A capable ofexecuting the command C001, the storage system 20A executes step S307and S309 described in the following.

The management server 50 receiving the interrogation then refers to thecommand-function correspondence table 104 and the function-devicecorrespondence table 105 it manages itself and retrieves the storagesystem 20C having the function A capable of executing the command C001(S305).

Next, the management server 50 notifies the storage system 20A that thestorage system 20 in possession of the function A capable of executingthe command C001 is the storage system 20C (S306).

Next, the storage system 20A transfers command C001 to the storagesystem 20C (S307). At this time, in the event that real data intended tobe processed by command C001 exists in the storage system 20A, thestorage system 20A sends the real data to the storage system 20C.Transmission of the real data may take place collectively a single timeor may be carried out partially split across a plurality of times. Inthe event that real data the command C001 intends to process exists inthe logical device 701 of the external storage system 70, supervision ofcontrol of the logical device 701 is changed from the storage system 20Ato the storage system 20C.

Next, the storage system 20A notifies the host computer 51 of normalreceipt of a command (S308).

After this, the storage system 20C notifies the storage system 20A ofcompletion at the stage where processing of command C001 is complete(S309).

The storage system 20A receiving notification of completion from thestorage system 20C then notifies the host computer 51 that theprocessing of command C001 is complete (S310).

Here, the network configuration of FIG. 1 is such that the networks (SAN41, 42) for issuing commands from the host computer 51 to each storagesystem 20 and the network (management network 40) for the managementserver 50 to transmit and receive management information between eachstorage system 20 are different outbound methods but this embodiment mayalso be applied to inbound methods. For example, this becomes an inboundmethod if a configuration is adopted where the management server 50transmits and receives management information to and from each storagesystem 20 via the SAN 41.

Next, a description is given with reference to FIG. 13 of commandmanagement executed by the host computer 51. Here, the host computer 51holds the alternate path software 61, the command-functioncorrespondence table 104, and the function-device correspondence table105, and is aware of the storage system 20 in possession of the functioncorresponding to the command and of the logical path connecting from thehost computer 51 to the logical device under the management of thestorage system 20.

While a command is issued, the host computer 51 refers to thecommand-function correspondence table 104 and the function-devicecorrespondence table 105 so as to retrieve which storage system 20 is inpossession of the function corresponding to this command (S401).

Next, the host computer 51 selects a logical device to connect to thehost computer 51 from the logical devices under the control of theretrieved storage system 20 and issues the command (S402). In this way,the host computer 51 can directly issue a command to the storage system20 in possession of the function corresponding to the command.

The host computer 51 may also issue a command by establishing a logicalpath in advance to all the logical devices under the control of thestorage system 20 and selecting a logical path connecting to a logicaldevice under the control of the storage system 20 in possession of thefunction corresponding to the command using the alternate path software61.

Next, a description is given with reference to FIG. 14 of commandmanagement executed by the virtualization device 52. Here, thevirtualization device 52 holds the alternate path software 61, thecommand-function correspondence table 104, and the function-devicecorrespondence table 105, and is aware of the storage system 20 inpossession of the function corresponding to the command and of thelogical path connecting from the virtualization device 52 to the logicaldevice under the management of the storage system 20.

When a command is received from the host computer 51, the virtualizationdevice 52 refers to the command-function correspondence table 104 andthe function-device correspondence table 105 so as to retrieve whichstorage system 20 is in possession of the function corresponding to thiscommand (S501).

Next, the virtualization device 52 selects a logical device connected tothe virtualization device 52 via the logical path from the logicaldevices under the control of the retrieved storage system 20 andtransfers a command (S502). In this way, the virtualization device 52can transfer a command to the storage system 20 in possession of thefunction corresponding to the command.

The virtualization device 52 may also transfer a command by establishinga logical path in advance to all the logical devices under the controlof the storage system 20 and selecting a logical path connecting to alogical device under the control of the storage system 20 in possessionof the function corresponding to the command using the alternate pathsoftware 61.

The command process shown in FIG. 14 may also be executed at avirtualization layer virtualizing a plurality of storage systems 20 intoa single virtual storage system 100.

Next, a description is given with reference to FIG. 15 of a commandprocess executed by the master service processor 82. Here, an example isshown where, in the event that the storage system 20 receiving thecommand from the host computer 51 does not have a function correspondingto this command, the master service processor 82 is interrogated as towhich storage system 20 has this function. The master service processor82 receiving this interrogation retrieves the storage system 20 havingthe function corresponding to this command and notifies the storagesystem 20 that is the destination of this interrogation. The storagesystem 20 receiving notification from the master service processor 82transfers the command to the storage system 20 having the functioncorresponding to this command.

The following (1) to (2) are presumed in the description of FIG. 15.

(1) It is necessary for the master service processor 82 to hold thecommand-function correspondence table 104 and the function-devicecorrespondence table 105 but it is not necessary for each storage system20 to hold the command-function correspondence table 104 and thefunction-device correspondence table 105.

(2) A storage system 20C having the function A is newly added to thevirtual storage system 100 comprised of storage system 20A and 20Bhaving the function B.

A process to add storage system 20C to the virtual storage system 100 isthen carried out (S601). Namely, a process to connect the storage system20C to the SAN 41 and recognize the host computer 51 and thevirtualization device 52 (for example, recognition of a storage systemidentifier of the storage system 20C, recognition of the LUN of alogical unit within the storage system 20C, and recognition of a pathnumber of a logical path connecting to this logical unit, etc.) iscarried out. In the event that the storage system 20C shares the logicaldevice 701 of the external storage system 70, the storage system 20 maybe connected to SAN 43.

Next, the master service processor 82 recognizes that a storage system20C is newly added to the virtual storage system 100, recognizes thatthe storage system 20C has a program P3, additionally registers afunction A to the command-function correspondence table 104 managed byitself, and additionally registers storage system 20C to thefunction-device correspondence table 105 managed by itself (S602).

Next, the host computer 51 sends command C001 corresponding to programP3 to the virtual storage system 100 (S603). The host computer 51 doesnot transmit the command C001 while individually recognizing theindividual storage systems 20A, 20B, 20C. Which of the storage systems20A, 20B and 20C receives the command is therefore decided on acase-by-case basis. Here, the description is continued assuming the casethat the storage system 20A receives the command C001.

Next, upon receiving the command C001, the storage system 20A determineswhether or not it is itself in possession of function A capable ofexecuting command C001. In this embodiment, the storage system 20A isnot in possession of function A capable of executing command C001 andtherefore interrogates the master service processor 82 as to whichstorage system 20 is in possession of the function A capable ofexecuting command C001 (S604).

If the storage system 20A is in possession of the function A capable ofexecuting the command C001, the storage system 20A executes step S307and S309 described in the following.

The master service processor 82 receiving the interrogation then refersto the command-function correspondence table 104 and the function-devicecorrespondence table 105 it manages itself and retrieves the storagesystem 20C having the function A capable of executing the command C001(S605).

Next, the master service processor 82 notifies the storage system 20Athat the storage system 20 in possession of the function A capable ofexecuting the command C001 is the storage system 20C (S606).

The storage system 20A then transfers command C001 to the storage system20C (S607). At this time, in the event that real data intended to beprocessed by command C001 exists in the storage system 20A, the storagesystem 20A sends the real data to the storage system 20C. Transmissionof the real data may take place collectively a single time or may becarried out partially split across a plurality of times. In the eventthat real data the command C001 intends to process exists in the logicaldevice 701 of the external storage system 70, supervision of control ofthe logical device 701 is changed from the storage system 20A to thestorage system 20C.

Next, the storage system 20A notifies the host computer 51 of normalreceipt of a command (S608).

After this, the storage system 20C notifies the storage system 20A ofcompletion at the stage where processing of command C001 is complete(S609).

The storage system 20A receiving notification of completion from thestorage system 20C then notifies the host computer 51 that theprocessing of command C001 is complete (S610).

In the above description, an example is shown of command managementwhere the master service processor 82 holds the command-functioncorrespondence table 104 and function-device correspondence table 105,but it is also possible for the service processor 81 to hold thecommand-function correspondence table 104 and function-devicecorrespondence table 105. However, as the service processor 81 isconnected to the respective storage systems 20, even if the serviceprocessor 81 is capable of determining whether or not it is a storagesystem 20 having a function corresponding to the command itself, it isnot capable of determining whether or not other storage systems 20 arestorage systems 20 having a function corresponding to the command. Withregards to this, the master service processor 82 is capable of managingfunctions of all of the storage systems 20 and is therefore capable ofdetermining which storage system 20 is a storage system 20 having afunction corresponding to the command.

Next, a description is given with reference to FIG. 16 of commandmanagement used by the command device 243. It is taken that thecommand-function correspondence table 104 and function-devicecorrespondence table 105 are stored in the memory 22 of each storagesystem 20 and the command device 243.

The host computer 51 writes the command C001 to the command device 243of the storage system 20A (S701).

When it is detected that command C001 has been written to the commanddevice 243, the CPU 21 of the storage system 20A refers to thecommand-function correspondence table 104 and function-devicecorrespondence table 105 stored in the memory 22 and the command device243 and retrieves the storage system 20C in possession of the function Acorresponding to the command C001 (S702).

In the event that the results of this retrieval determine that thefunction A corresponding to the command C001 is not an own function butrather is a function of another storage system 20C, the storage system20A does not send the command C001 back to the host computer 51 butrather extends the command process and transfers the command C001 to thecommand device 243 of the storage system 20C (S703).

In the event that the command received by the command device 243 of thestorage system 20A is transferred to the storage system 20C, transfertakes place to the command device 243 of the storage system 20C usingthe method with which the command device 243 received the command. Inthis case, the command device 243 of the storage system 20C has a methodfor detecting the storage system 20A. In the event that there is nocommand device 243 at the storage system 20C, it is possible to transferthe command from the storage system 20A to the storage system 20C afterconverting the command to a format recognizable by the storage system20C.

Next, a description is given with reference to FIG. 17 of a process forcarrying out command management as a result of the host computer 51re-issuing a command. When a command is received from the host computer51, the storage system 20A retrieves a storage system 20 in possessionof the function corresponding to the command (FIG. 11: S208). Thestorage system 20A then requests re-issuance of the command to the hostcomputer 51 and notifies the host computer 51 of which storage system 20is in possession of the function corresponding to the command. The hostcomputer 51 receiving the command reissue request then re-issues thecommand to the storage system in possession of the functioncorresponding to the command.

The host computer 51 then issues the command C001 to the storage system20A (S801).

Next, the storage system 20A refers to the command-functioncorrespondence table 104 and function-device correspondence table 105managed by itself and retrieves the storage system 20C in possession ofthe function A corresponding to the command C001 (S802).

The storage system 20A requests re-issue of the command C001 to the hostcomputer 51 and, notifies the host computer 51 that the storage system20 in possession of the function A corresponding to the command C001 isthe storage system 20C (S803).

The host computer 51 then receives the command re-issue request andnotification that the storage system 20 in possession of the function Acorresponding to the command C001 is the storage system 20C from thestorage system 20A (S804).

Next, the host computer 51 re-issues the command C001 to the storagesystem 20C (S805). At this time, in the event that real data intended tobe processed by command C001 exists in the storage system 20A, thestorage system 20A sends the real data to the storage system 20C.Transmission of the real data may take place collectively a single timeor may be carried out partially split across a plurality of times. Inthe event that real data the command C001 intends to process exists inthe logical device 701 of the external storage system 70, supervision ofcontrol of the logical device 701 is changed from the storage system 20Ato the storage system 20C.

In the above description, an example is shown where the storage system20A retrieves which storage system 20 is in possession of the functioncorresponding to the command issued by the host computer 51 but it isalso possible for this to be retrieved by the management server 50 ormaster service processor 82, with the host computer 51 being notified ofcommand re-issue requests and retrieval results etc.

Further, a command re-issue request is by no means essential to theprocess of FIG. 17. The host computer 51 may also re-issue the commandC001 to the storage system 20C at the stage of receiving notificationthat the storage system 20 in possession of the function A correspondingto the command C001 is the storage system 20C from the storage system20A.

In cases where a plurality of storage systems 20 in possession of thefunction corresponding to the command issued by the host computer 51exist in each of the processes shown in FIG. 11 to FIG. 17, it ispreferable to transfer commands to storage systems 20 of a low rate ofoperation (busy rate), storage systems 20 related to the task, or tostorage systems 20 that were not selected on the previous occasion, etc.

Further, in the above description, the case where the functioncorresponding to the command is implemented by a single storage system20 is supposed but this embodiment is also applicable to cases where thefunction corresponding to the command is implemented by two or morestorage systems 20. For example, it is necessary for a storage system 20of a local site (copy source) and a storage system 20 of a remote site(copy destination) to be loaded with a remote copy function to executeremote copying. For example, in the event that a storage system 20C thatis not in possession of a remote copy function receives a remote copyrequest, the storage system 20C may retrieve the storage systems 20A,20B in possession of the remote copy function, transfer the remote copycommand from the storage system 20C to the storage systems 20A, 20B, andexecute remote copying between the storage system 20A and the storagesystem 20B.

Next, a description is given with reference to FIG. 18 of a process forwhen a fault occurs during transfer of a command in the method of FIG.11 to FIG. 16. Here, a description is given of an example where a faultoccurs at the storage system 20C and the host computer 51 issues thecommand C001 to the storage system 20A directly after notification of afault report from the storage system 20C to the management server 50(i.e. when the host computer 51 and the storage system 20B do notrecognize the fault of the storage system 20C).

When a fault occurs at the storage system 20C, the storage system 20Creports the fault to the management server 50 (S901).

Next, the host computer 51 issues the command C001 to the storage system20A prior to recognizing the fault of the storage system 20C (S902).

After this, the storage system 20A refers to the command-functioncorrespondence table 104 and function-device correspondence table 105managed by itself and retrieves the storage system 20C in possession ofthe function A corresponding to the command C001 (S903).

The storage system 20A then transfers command C001 to the storage system20A (S904).

However, an error is sent back from the storage system 20C to thestorage system 20A because there is a fault at the storage system 20C(S905).

The storage system 20A then recognizes the storage system 20C is faultyas a result of receiving the error report from the storage system 20C,and the “status” of the storage system 20C of the fault information 107is updated to “faulty” (S906).

If another storage system 20 in possession of the function Acorresponding to the command C001 exists (S907: YES), the storage system20A returns to the process of step S903.

On the other hand, if another storage system 20 in possession of thefunction A corresponding to the command C001 does not exist (S907: NO),the storage system 20A reports an error to the host computer 51 (S908).

Next, the storage system 20A reports the fault of the storage system 20Cto the management server 51 (S909). When the fault report is receivedfrom the storage system 20A, the management server 51 updates the“status” of the storage system 20C of the fault information 107 managedby itself to “faulty”.

Next, a description is given with reference to FIG. 19 of anotherprocess for when a fault occurs during transfer of a command in themethod of FIG. 11 to FIG. 16. Here, a description is given of an exampleof a case where the command C001 is issued from the host computer 51 tothe storage system 20A after a fault occurs at the storage system 20C,the management server 50 is notified of a fault report by the storagesystem 20C, and each of the storage systems 20 are notified of the faultreport by the management server 51 (i.e. when each storage system 20recognizes the fault of the storage system 20C).

When a fault occurs at the storage system 20C, the storage system 20Creports the fault to the management server 50 (S1001).

Next, the management server 50 notifies all of the storage systems 20within the virtual storage system 100 of the fault of the storage system20C (S1002).

Each storage system 20 then recognizes that the storage system 20C iscurrently faulty from the notification from the management server 50 andupdates the “status” of the storage system 20C of the fault information107 to “faulty” (S1003).

Next, the host computer 51 issues the command C001 to the storage system20A prior to recognizing the fault of the storage system 20C (S1004).

Next, the storage system 20A refers to the command-functioncorrespondence table 104 and function-device correspondence table 105managed by itself, retrieves the storage system 20C in possession of thefunction A corresponding to the command C001, refers to the faultinformation 107, and recognizes that the storage system 20C is faulty(S1005).

The storage system 20A then reports an error to the host computer 51(S1006).

In step S1005, in the event that a plurality of storage systems 20 inpossession of a function A corresponding to the command C001 exist, thestorage system 20A may also transfer the command C001 to a storagesystem 20 operating normally.

Next, a description is given with reference to FIG. 20 of loaddistribution within the virtual storage system 100. Here, an example isshown of the case where the load on the storage system 20C of theplurality of storage systems 20 within the virtual storage system 100 islarge.

The management server 50 acquires load information from each of thestorage systems 20 within the virtual storage system 100 and recognizesthat the load is concentrated on the storage system 20C (S1101).Resource rate of operation and occupancy rate of each storage system 20etc. exists as load information.

Next, the management server 50 notifies the storage system 20C that theload is concentrated on the storage system 20C (S1102).

After this, the storage system 20C selects logical devices that are notusing the program P3 only installed on the storage system 20C(hereinafter referred to as transfer candidate logical devices) aslogical devices that are transfer candidates (S1103). The reason logicaldevices that are not using the program P3 installed only on storagesystem 20C are selected as transfer candidate logical devices is becausethere is no load dispersion in the case where the load on the program P3installed only on storage system 20C is large even if a logical deviceusing the program P3 is selected as a logical device that is a candidatefor transfer.

Next, the storage system 20C notifies the management server 50 oftransfer of the transfer candidate logical device (S1104).

The management server 50 then refers to the resource rate of operationof each storage system 20 and determines a transfer destination storagesystem 20 for the transfer candidate logical device (S1105). Here, anexample is shown of the case where storage system 20A is selected as thetransfer destination storage system 20.

Next, the management server 50, in addition to designating the storagesystem 20A of the transfer destination at the storage system 20C,transmits a transfer instruction for the transfer candidate logicaldevice (S1106).

Next, the storage system 20C transfers the transfer candidate logicaldevice to the transfer destination storage system 20A under theinstruction of the management server 50 (S1107).

Which storage system 20 is made the transfer destination storage system20 may be inputted to the storage system 20C by a system administratorvia the service processor 81 or may be designated by the host computer51 to be the storage system 20C.

A command process taking into consideration differences in performanceof the plurality of storage systems 20 constituting the virtual storagesystem 100 is described with reference to FIG. 21 and FIG. 22. In theevent that there are differences in performance between the plurality ofstorage systems 20 constituting the virtual storage, it is possible toimprove the overall processing performance of the virtual storage system100 by having the high-performance storage systems process the bulk ofthe I/O requests.

FIG. 21 shows specification information 109. The specificationinformation 109 is comprised of processing power, port performance, andcaching capacity, etc. of each storage system 20A, 20B, 20C. Thespecification information 109 is stored in the memory 22 of each storagesystem 20, the management server 50, the master service processor 82,and the service processor 81, etc.

Next, a command process taking into consideration differences inperformance of the plurality of storage systems 20 is described withreference to FIG. 22. Here, an example is shown of the case where eachstorage system 20 holds the specification information 109.

When the command is received from the host computer 51 (S1201), thestorage system 20A refers to the specification information 109 andretrieves high-performance storage systems from the virtual storagesystem 100 (S1202). Here, an example is shown where the storage system20C is a high-performance storage system.

The storage system 20A transfers the command from the host computer 51to the storage system 20C (S1203). It is then possible to improve theoverall processing performance of the virtual storage system 100 byhaving the high-performance storage system process a large number ofcommands. For example, with a usual host access, it is preferable for asmuch processing as possible to be carried out at the high-performancestorage system 20C, with processes such as I/O processes such as copyingetc. (that do not require high-performance) being carried out at theother storage system 20A.

It is preferable for what extent the high-performance storage system 20Cand the other storage system 20A process I/O requests to be determinedusing a ratio identifying the difference in performance of thehigh-performance storage system 20C and the other storage system 20A.For example, if the caching capacity of the high-performance storagesystem 20C is twice the caching capacity of the other storage system20A, the number of I/O processes of the high-performance storage system20C is made to be twice the number of I/O processes of the other storagesystem 20A.

A command process taking into consideration differences in rate ofoperation of the plurality of storage systems 20 constituting thevirtual storage system 100 is described with reference to FIG. 23 andFIG. 24. In the event that there are differences in rate of operationbetween the plurality of storage systems 20 constituting the virtualstorage system 100, it is possible to improve the overall processingperformance of the virtual storage system 100 by having the low rate ofoperation storage systems 20 process the bulk of the I/O requests.

FIG. 23 shows rate of operation information 110. The rate of operationinformation 110 contains the range of operation of each storage system20A, 20B, 20C (the processor usage rate of CPU 22, the number of I/Oprocesses (IOPS) occurring per unit time of the CPU 22, the datatransfer amount (transfer rate) per unit time of the interface controlsection 26, and the time (response time) between the storage system 20receiving an I/O request from the host computer 51 and making aresponse, etc.). The rate of operation information 110 is stored in thememory 22 of each storage system 20, the management server 50, themaster service processor 82, and the service processor 81, etc.

Next, a command process taking into consideration differences in rate ofoperation of the plurality of storage systems 20 is described withreference to FIG. 24. Here, an example is shown of the case where eachstorage system 20 holds rate of operation information 110.

When the command is received from the host computer 51 (S1301), thestorage system 20A refers to the rate of operation information 110 andretrieves a low rate of operation storage system 20 from within thevirtual storage system 100 (S1302). Here, an example is shown of thecase where the rate of operation of the storage system 20C is low.

The storage system 20A transfers the command from the host computer 51to the storage system 20C (S1303). It is then possible to improve theoverall processing performance of the virtual storage system 100 byhaving the low rate of operation storage system 20C process a largenumber of commands. For example, with a usual host access, it ispreferable for as much processing as possible to be carried out at thelow rate of operation storage system 20C, with processes such as I/Oprocesses such as copying etc. (that do not require a low rate ofoperation) being carried out at the other storage system 20A.

It is preferable for what extent the low rate of operation storagesystem 20C and the other storage system 20A process I/O requests to bedetermined using a ratio identifying the difference in rate of operationof the low rate of operation storage system 20C and the other storagesystem 20A. For example, if the rate of operation of the storage system20C is half of the rate of operation of the other storage system 20A,the number of I/O processes of the storage system 20C is made to betwice the number of I/O processes of the other storage system 20A.

If, while implementing a command process (FIG. 22) taking intoconsideration differences in performance of the storage systems 20 orimplementing a command process (FIG. 24) taking into considerationdifferences in the rate of operation of the storage systems 20, if I/Orequests intended for processing by the storage system 20A are processedby the storage system 20C, it is preferable for a logical device storingreal data to be moved from the storage system 20A to the storage system20C, and for an I/O request to be issued from the host computer 51 tothe storage system 20C. In the event that real data is stored in theexternal storage system 70, it is preferable to switch supervision ofcontrol of the external storage system 70 over from the storage system20A to the storage system 20C.

Further, “a main section retrieving a high-performance system” or “amain section retrieving a low rate of operation storage system” is notlimited to each of the storage systems 20 and may also be, for example,the management server 50, the service processor 81, the master serviceprocessor 82, the host computer 51, or the virtualization device 52.Namely, the processing procedure while the storage system 20A receivingthe command from the host computer 51 transfers the command to thestorage system 20C in the process of FIG. 11 to FIG. 20 described abovemay conform to a method of substituting “retrieval of a storage systemhaving a function corresponding to a command” with “retrieval ofhigh-performance storage system” or “retrieval of low rate of operationstorage system”.

FIG. 25 shows a system configuration of a virtual storage system 101.Devices etc. with the same numerals as numerals shown in FIG. 1 are thesame devices etc. and detailed description thereof is therefore omitted.The virtual storage system 101 virtualizes the plurality of storagesystems 20A, 20B, 20C into a single storage system 101. The point ofdistinction with the virtual storage system 100 shown in FIG. 1 is thatthe virtual storage system 101 does not have an external storage system70. Namely, each storage system 20 has a real device for storing realdata. It is also possible to carry out processes (processes shown inFIG. 11 to FIG. 22) such as the command management and fault processingetc. described above for the virtual storage system 101.

According to this embodiment, it is possible to process commands from ahost computer 51 in an appropriate manner even in cases where thefunctions in the possession of each storage system 20 are different invirtual storage systems 100, 101 virtualizing a plurality of storagesystems 20 as a single storage resource. Further, it is possible toshare functions of each storage system 20 for the virtual storagesystems 100, 101 as a whole even in cases where new and old storagesystems 20 are mixed up so that the functions of each storage system 20are different.

1. A computer system comprises: a first storage system and a secondstorage system each coupled to a host computer, wherein the firststorage system is coupled to the host computer without the secondstorage system being interposed between the first storage system and thehost computer, and wherein the second storage system is coupled to thehost computer without the first storage system being interposed betweenthe second storage system and the host computer, the first and secondstorage systems each having first correspondence information regardingcorrespondence relationships between commands from the host computer andfunctions of the first and the second storage systems and secondcorrespondence information regarding correspondence relationshipsbetween the functions and the storage systems that have the functions, athird storage system coupled to the first storage system and the secondstorage system, wherein one of the first and the second storage systemsis configured to provide a logical volume stored in the third storagesystem as a virtual volume to the host computer, wherein the hostcomputer is configured to recognize the first and the second storagesystems logically as a single virtual storage system, and wherein one ofthe first and the second storage systems is configured to: receive acommand from the host computer to the virtual storage system; determinewhich of the storage systems possesses the function corresponding to thecommand by referring to the first and second correspondence information;if said one of the first and the second storage systems has possessionof the function, execute the command; and if said one of the first andthe second storage systems does not have possession of the function,transfer the command to the other one of the first and the secondstorage systems in possession of the function corresponding to thecommand by referring to the second correspondence information.
 2. Thecomputer system according to claim 1, wherein each of the first andsecond storage systems further comprises a command device, wherein eachof the command devices is written with the command and is configured toexecute the retrieving and the transferring.
 3. The computer systemaccording to claim 2, wherein, if either of the first and second storagesystems does not have possession of the function, the first and secondstorage systems are configured to request a re-issue of the commandwhose destination is one of the first and second storage systems whichhas the possession of the function.
 4. The computer system according toclaim 3, wherein, if one of the first and second storage systemsreceives an indication of error from the other one of the first andsecond storage systems after transferring the command, said one of thefirst and second storage systems is configured to determine the otherone of the first and second storage systems, except the storage systemwhich issued the error, in possession of the function corresponding tothe command by referring to the second correspondence information and totransfer the command to the other one of the first and second storagesystems.
 5. A computer system comprises: a first storage system and asecond storage system each coupled to a host computer, wherein the firststorage system is coupled to the host computer without the secondstorage system being interposed between the first storage system and thehost computer, and wherein the second storage system is coupled to thehost computer without the first storage system being interposed betweenthe second storage system and the host computer, the first and secondstorage systems, a virtualization device for virtualizing the first andsecond storage systems into a single storage resource provided to thehost computer, each of the first and second storage systems having firstcorrespondence information regarding correspondence relationshipsbetween commands from the host computer and functions of the first andthe second storage systems and second correspondence informationregarding correspondence relationships between the functions and thestorage system that have the functions, wherein the virtualizationdevice is coupled to the first and second storage systems and the hostcomputer, a third storage system coupled to the first storage system andthe second storage system, wherein one of the first and the secondstorage system is configured to provide a logical volume stored in thethird storage system as a virtual volume to the host computer, whereinthe host computer is configured to recognize the first and the secondstorage systems logically as a single virtual storage device, whereinthe virtualization device is configured to: receive a command from thehost computer to the virtual storage device; determine which of thestorage systems possesses the function corresponding to a command byreferring to the first and second correspondence information; andtransfer the command to one of the first and the second storage systemsin possession of the function corresponding to the command by referringto the second correspondence information.
 6. The computer systemaccording to claim 5, wherein each of the first and second storagesystems further comprises a command device, wherein each of the commanddevices is written with the command from the host computer, and whereineach of the command devices includes the first correspondenceinformation and the second correspondence information, and is configuredto: retrieve possession of the function corresponding to the command byreferring to the first correspondence information and, if one of thefirst and second storage systems which comprises one of the commanddevices written with the command does not have possession of thefunction, to transfer the command to the other one of the first andsecond storage systems in possession of the function corresponding tothe command by referring to the second correspondence information. 7.The computer system according to claim 5, wherein, if either of thefirst and second storage systems does not have possession of thefunction, the first and second storage systems are configured torequests a re-issue of the command whose destination is one of the firstand second storage systems which has possession in the function.
 8. Thecomputer system according to claim 7, wherein, if one of the first andsecond storage systems receives an indication of error from the otherone of the first and second storage system after transferring thecommand, said one of the first and second storage systems is configuredto determine the other one of the first and second storage systems,except the storage system which issued the error, in possession of thefunction corresponding to the command by referring to the secondcorrespondence information and to transfer the command to the other oneof the first and second storage systems.